Re: [RFC 07/37] KVM: s390: protvirt: Secure memory is not mergeable

[David Hildenbrand <david@xxxxxxxxxx>]

On 24.10.19 18:33, Claudio Imbrenda wrote:
> On Thu, 24 Oct 2019 18:07:14 +0200
> David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> > On 24.10.19 13:40, Janosch Frank wrote:
> > > KSM will not work on secure pages, because when the kernel reads a
> > > secure page, it will be encrypted and hence no two pages will look
> > > the same.
> > >
> > > Let's mark the guest pages as unmergeable when we transition to
> > > secure mode.
> > >
> > > Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
> > > ---
> > >    arch/s390/include/asm/gmap.h |  1 +
> > >    arch/s390/kvm/kvm-s390.c     |  6 ++++++
> > >    arch/s390/mm/gmap.c          | 28 ++++++++++++++++++----------
> > >    3 files changed, 25 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/arch/s390/include/asm/gmap.h
> > > b/arch/s390/include/asm/gmap.h index 6efc0b501227..eab6a2ec3599
> > > 100644 --- a/arch/s390/include/asm/gmap.h
> > > +++ b/arch/s390/include/asm/gmap.h
> > > @@ -145,4 +145,5 @@ int gmap_mprotect_notify(struct gmap *,
> > > unsigned long start,
> > >    void gmap_sync_dirty_log_pmd(struct gmap *gmap, unsigned long
> > > dirty_bitmap[4], unsigned long gaddr, unsigned long vmaddr);
> > > +int gmap_mark_unmergeable(void);
> > >    #endif /* _ASM_S390_GMAP_H */
> > > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> > > index 924132d92782..d1ba12f857e7 100644
> > > --- a/arch/s390/kvm/kvm-s390.c
> > > +++ b/arch/s390/kvm/kvm-s390.c
> > > @@ -2176,6 +2176,12 @@ static int kvm_s390_handle_pv(struct kvm
> > > *kvm, struct kvm_pv_cmd *cmd) if (r)
> > >    			break;
> > >    
> > > +		down_write(&current->mm->mmap_sem);
> > > +		r = gmap_mark_unmergeable();
> > > +		up_write(&current->mm->mmap_sem);
> > > +		if (r)
> > > +			break;
> > > +
> > >    		mutex_lock(&kvm->lock);
> > >    		kvm_s390_vcpu_block_all(kvm);
> > >    		/* FMT 4 SIE needs esca */
> > > diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> > > index edcdca97e85e..bf365a09f900 100644
> > > --- a/arch/s390/mm/gmap.c
> > > +++ b/arch/s390/mm/gmap.c
> > > @@ -2548,6 +2548,23 @@ int s390_enable_sie(void)
> > >    }
> > >    EXPORT_SYMBOL_GPL(s390_enable_sie);
> > >    
> > > +int gmap_mark_unmergeable(void)
> > > +{
> > > +	struct mm_struct *mm = current->mm;
> > > +	struct vm_area_struct *vma;
> > > +
> > > +	for (vma = mm->mmap; vma; vma = vma->vm_next) {
> > > +		if (ksm_madvise(vma, vma->vm_start, vma->vm_end,
> > > +				MADV_UNMERGEABLE, &vma->vm_flags))
> > > {
> > > +			mm->context.uses_skeys = 0;
> >
> > That skey setting does not make too much sense when coming via
> > kvm_s390_handle_pv(). handle that in the caller?
>
> protected guests run keyless; any attempt to use keys in the guest will
> result in an exception in the guest.

still, this is the recovery path for the "mm->context.uses_skeys = 1;" 
in enable_skey_walk_ops() and confuses reader (like me).


--

Thanks,

David / dhildenb